docs: *_GATEWAY_DOMAINS env vars (#73)

* docs: RAINBOW_SUBDOMAIN_GATEWAY_DOMAINS env var
* docs: add RAINBOW_GATEWAY_DOMAINS

---------

Co-authored-by: Marcin Rataj <lidel@lidel.org>

.gitignore

@@ -2,6 +2,7 @@ rainbow
 libp2p.key
 blockstore
 datastore
+flatfs
 
 # Binaries for programs and plugins
 *.exe

docs/environment-variables.md

@@ -3,6 +3,8 @@
 `rainbow` ships with some implicit defaults that can be adjusted via env variables below.
 
 - [Configuration](#configuration)
+  - [`RAINBOW_GATEWAY_DOMAINS`](#rainbow_gateway_domains)
+  - [`RAINBOW_SUBDOMAIN_GATEWAY_DOMAINS`](#rainbow_subdomain_gateway_domains)
   - [`KUBO_RPC_URL`](#kubo_rpc_url)
 - [Logging](#logging)
   - [`GOLOG_LOG_LEVEL`](#golog_log_level)
@@ -15,15 +17,29 @@
 
 ## Configuration
 
+### `RAINBOW_GATEWAY_DOMAINS`
+
+Comma-separated list of path gateway hostnames. For example, passing `ipfs.io` will enable handler for standard [path gateway](https://specs.ipfs.tech/http-gateways/path-gateway/) requests with the `Host` header set to `ipfs.io`.
+
+Default: `127.0.0.1`
+
+
+### `RAINBOW_SUBDOMAIN_GATEWAY_DOMAINS`
+
+Comma-separated list of [subdomain gateway](https://specs.ipfs.tech/http-gateways/subdomain-gateway/) domains. For example, passing `dweb.link` will enable handler for standard [subdomain gateway](https://specs.ipfs.tech/http-gateways/subdomain-gateway/) requests with the `Host` header set to `*.ipfs.dweb.link` and  `*.ipns.dweb.link`.
+
+Default: `localhost`
 
 ### `KUBO_RPC_URL`
 
-Default: see `DefaultKuboRPC`
+Default: `127.0.0.1:5001` (see `DefaultKuboRPC`)
 
-Single URL or a comma separated list of RPC endpoints that provide `/api/v0` from Kubo.
+Single URL or a comma separated list of RPC endpoints that provide legacy `/api/v0` from Kubo.
 
 We use this to redirect some legacy `/api/v0` commands that need to be handled on `ipfs.io`.
 
+This is deprecated and will be removed in the future.
+
 ## Logging
 
 ### `GOLOG_LOG_LEVEL`
@@ -79,7 +95,6 @@ tracing is disabled.
 
 Warning: Enabling tracing will likely affect performance.
 
-
 ## Testing
 
 ### `GATEWAY_CONFORMANCE_TEST`